Earlier results from our laboratory showed that the steroid hormone ecdysone has an essential role throughout Drosophila development. This proposal is concerned with a genetic and molecular study of the regulation of transcription of certain ecdysone-inducible genes in highly differentiated larval fat bodies and also of other genes that apparently are not ecdysone-inducible. The inducible systems involve the PI and Lsp-2 genes, each of which map at a single site on the third-chromosome. Rapid transcription of these genes begins late in the third-instar larval stage, specifically in the fat bodies. We have isolated several cloned genomic segments containing the structural genes and also extensive flanking sequences for the P1 and Lsp-2 systems. We are examining the organization of the cloned DNA by restriction endonuclease mapping, base sequence analyses and heteroduplex mapping. A search for regulatory proteins that bind to the cloned DNA is progress. Mutants are being isolated that map in the regions of the two genes, and these are being tested for detects in the structure or function of the genes or gene products in order to identify mutants affecting the two genes. Similar studies are in progress for the Lsp-1 system which has three separate and unlinked structural genes, one for each of the subunits of the multimeric Lsp-1 protein. We have isolated cloned genomic segments containing two of the structural genes, and have obtained preliminary evidence for a DNA sequence common to the two genes that might function as a regulatory site. Our goal is to elucidate all of the steps and interacting components involved in the stage-specific and tissue-specific regulation of transcription for the three Drosophila systems, and in particular the role of ecdysone in initiating transcription of the two ecdysone-inducible systems.